THE BACTERIOPHAGE IN THE HEALTHY INDIVIDUAL 239 



comparable to those cited. In three others a bacteriophage was 

 not found; if it was present it was inactive for the eight test 

 organisms. 



Nos. 16 and 17. Swine in Cochin-China, in a barbone area. 



Nos. 18 and 19. Swine in Paris. 



Nos. 20 and 21. Swine in France, on a farm infected with 

 avian typhosis (4 other comparable results). 



Nos. 22 and 23. Rabbits living in cages at the Pasteur Insti- 

 tute (4 other comparable findings). 



Nos. 24 and 25. Goats in Paris. 



CONCLUSIONS 



In brief, in all the healthy animals examined the presence of 

 a bacteriophage possessing virulence for one or another of the 

 intestinal bacteria selected as test organisms has been demonstrated. 



These examinations show that in an epizootic area the intestinal 

 bacteriophage of refractory animals is generally possessed of viru- 

 lence for the bacterium causing the epidemic; on the contrary, 

 this is never observed outside of the foci of infection. 



The activity of the bacteriophagous ultramicrobe towards a 

 given bacterium can only be explained as the result of growth at 

 the expense of this bacterium. Tests of the virulence of the ul- 

 tramicrobe in animals inhabiting an epizootic region or living in 

 an area free of the infection, against the bacterium considered 

 as the cause of the disease, are, among other proofs, conclusive 

 in this respect. The experiments in vitro are in accord with the 

 facts observed in animals. All the facts agree in showing that 

 in the body the bacteriophage ceases to be active for a bacterium 

 a few days after the destruction of this bacterium. With ani- 

 mals, the ingestion of typhoid, paratyphoid, and especially, 

 dysentery bacilli, must be extremely frequent, since in animals 

 the intestinal bacteriophage is, except in rare instances, virulent 

 for one or another of these organisms. 



The sum total of the results suggests that the bacteriophage 

 possesses " co-virulences" or " accessory virulences" extending 

 to organisms belonging to the same group as the invading bacillus. 

 For example, a bacteriophage increasing its virulence for the Shiga 

 strain of B. dysenteriae must at the same time, although to a less 



